1. Field of the Invention
The present invention relates to the drive control of a motor vehicle, and more particularly to a drive control system for a motor vehicle in which a braking force is also controllable in accordance with the manipulation or movement of an accelerator pedal.
2. Description of the Prior Art
In general, the accelerator pedal of a motor vehicle is directly connected with the throttle valve of the engine of the vehicle. Accordingly, the control of the manipulated variable (or pressed magnitude) of the accelerator is, or means the very control of the opening (or opening degree) of the throttle. A manipulated accelerator variable (or accelerator stroke) of 0% corresponds to a throttle opening of 0% (full closure). Therefore, a braking force which acts when the accelerator pedal has been released or eased up is based only on engine braking which conforms to a gearshift stage held at that time as it is.
In contrast, a motor vehicle furnished with a throttle valve which is controlled independently of the accelerator pedal is disclosed in, for example, the official gazette of Japanese Patent Application Laid open No. 162570/1993. According to the control of the vehicle, when the accelerator pedal has been released, it is judged that the driver of the vehicle is requesting an engine braking force. Then, when a vehicle speed increases more than at the release of the accelerator pedal under a downslope for example, an automatic transmission is automatically downshifted to increase the engine braking force.
With the prior-art example, the "driving force" of the motor vehicle can be really controlled by the accelerator manipulation. However, the occasion where the manipulated accelerator variable is zero is merely regarded as the occasion where the braking force is required, and it cannot be said that the control is adapted to establish a "braking force" reflecting the driver's request. Naturally, therefore, the braking force is not controlled as the driver's intention by the accelerator manipulation, and it needs to be controlled by pressing a brake pedal separately from the accelerator pedal.